JP2931301B1 - Method for growing transition metal oxide single crystal - Google Patents

Abstract

Abstract: A large oxide single crystal containing Ru or Rh is grown under stable conditions. When growing a single crystal of an oxide containing Ru or Rh as the transition metal element T, the transition metal having the same valence as the valence of the transition metal element T in the target transition metal oxide or a valence equivalent thereto T-containing oxide T _x O _y ( _x , _y
Is a positive integer) to adjust the growth atmosphere to an oxygen partial pressure that can stably exist at the growth temperature. As transition metal oxide single crystals, RuO ₂ , SrRuO ₃ , CaRuO ₃ , Ca
₂ RuO ₄ , Sr ₃ Ru ₂ O ₇ , Ca ₃ Ru ₂ O ₇ , R
h ₂ O ₃ , Sr ₂ RhO ₄ , Ca ₂ RhO ₄ , SrRh
O ₃ , CaRhO ₃ , Sr ₃ Rh ₂ O ₇ , Ca ₃ Rh ₂
O _{7 and the} like. When growing this type of oxide single crystal by the floating zone method, the growth atmosphere is adjusted to an oxygen partial pressure at which RuO ₂ or Rh ₂ O ₃ can stably exist at the growth temperature. [Effect] RuO ₂ → Ru + O ₂ or Rh ₂ O ₃ → Rh + O
_Since the decomposition reaction of ₂ is suppressed, a transition metal oxide single crystal having a target composition can be stably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transition metal oxide useful as a functional single crystal material composed of a transition metal oxide or a single crystal substrate used for laminating thin films of semiconductors, magnetic materials, superconductors and the like. The present invention relates to a method for growing a single crystal.

[0002]

_2. Description of the Related Art Ruthenium oxide Sr ₂ RuO ₄ having a layered perovskite structure similar to a copper oxide high-temperature superconductor
Has recently been found to have the property of undergoing a superconducting transition at 1K. Since then, comparative studies between Sr ₂ RuO ₄ and copper oxide high-temperature superconductor have been actively conducted. RuO ₂ having a rutile structure similar to a perovskite structure is
Since it shows high conductivity despite being an oxide, LS
It has been widely studied as an electrode material for I (large scale integrated circuit). SrR with perovskite structure
uO ₃ is known as a typical ferromagnet exhibiting a transition at 160K. It is rare that a transition metal oxide having a perovskite structure and exhibiting a ferromagnetic transition is rare. SrRuO ₃ in a ferromagnetic state has been reported to exhibit the same large magneto-optical effect as the ferromagnetic metals Fe, Co, and Ni. [L. Klein et al. , Appl. Phys
s. Lett. 66, 2427 (1995)]. Focusing on this magneto-optical effect, vigorous magneto-optical studies using SrRuO ₃ thin films have been conducted.

In research on ferroelectric capacitors which are indispensable for the fabrication of LSI memories, degradation characteristics and charge leakage characteristics have been examined for the ferroelectric material Pb (Zr, Ti) having a perovskite structure deposited on a SrRuO ₃ thin film. ) O ₃ has been reported to exhibit very good properties [C.
B. Eom et al. , Appl. Phys. Le
tt. 63, 2570 (1993)]. Thus, L
In the research of electrode materials and the study of magneto-optical materials in SI, the necessity of the above-mentioned large oxide single crystal of Ru oxides, especially SrRuO ₃ , has become extremely high. in addition,
A substance having a perovskite structure or a structure similar to perovskite (for example, SrTiO ₃ , LaSrAlO ₄ )
The single-crystal substrate has good crystal structure consistency with the high-temperature superconductor, and is therefore often used as a substrate for depositing a new functional material such as a high-temperature superconductor thin film or various magnetic materials. Moreover, SrR
Since uO ₃ has a perovskite crystal structure as described above, it not only satisfies the necessary conditions as a substrate for depositing a high-temperature superconductor thin film, a magnetic material thin film, and a functional material thin film, but also has a ferromagnetic material at 160 K or less. Research on heterostructures of various thin films and ferromagnetic materials is expected by utilizing the above.

[0004]

There have been several reports on the growth of single crystals of perovskite-related Ru oxide (for example, RJ Boucha).
rd et al. . Mat. Res. Bull. 7,
873 (1972)). However, in either report, SrCl ₂ or CaCl ₂ is grown as a flux. The size of the grown crystal is, for example, 1 mm.
It has a size of only × 1 mm × 1 mm and has a size suitable for use as a substrate, but has not been obtained at present. At present, the growth of a relatively large Ru oxide single crystal is limited to the growth of the superconductor Sr ₂ RuO _{4 by} the floating zone method. In a situation where a perovskite-related Ru oxide is attracting attention, no research has been reported on growing a large single crystal having a size that can be used as a single crystal substrate. However, if an oxide of Ru or Rh can be grown to a size practical as a single crystal substrate, Ru or Rh can be grown.
Utilizing the superconducting characteristics, the magnetic characteristics such as the magneto-optical effect, the effect on ferroelectrics, etc. of the oxides, various functional materials that have never been seen before can be provided.

[0005]

SUMMARY OF THE INVENTION The present invention has been devised to meet such a demand, and is used as a functional material or for laminating thin films of semiconductors, magnetic materials, superconductors and the like. An object is to grow a large single crystal of a Ru oxide and a Rh oxide useful as a substrate material to be used. The present invention achieves the object, when growing a single crystal of an oxide containing Ru or Rh as the transition metal element T, the same valence as the valence of the transition metal element T in the target transition metal oxide or oxide T _x O _y containing a transition metal T with a valence analogous thereto (x, y is a positive integer) is characterized by adjusting the growth atmosphere to an oxygen partial pressure which can exist stably at a temperature at the time of development And

As transition metal oxide single crystals, RuO
_Two , SrRuO_Three , CaRuO_Three , Ca_Two RuO_Four , S
r_Three Ru_Two O₇ , Ca_Three Ru_Two O₇ , Rh_Two O_Three , Sr
_Two RhO_Four , Ca_Two RhO_Four , SrRhO_Three , CaRh
O_Three , Sr_Three Rh_Two O₇ , Ca _Three Rh_Two O₇ Etc.
When growing this type of oxide single crystal by the floating zone method,
RuO_Two Or Rh_Two O_Three At the temperature at the time of growth
The growth atmosphere is adjusted to an oxygen partial pressure that can exist stably. acid
Growth atmosphere with adjusted elemental pressure is effective for melt stability
The present invention is applicable to the pulling method.
You.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In growing a single crystal from a polycrystalline oxide sintered body containing Ru or Rh as a transition metal by a floating zone method,
The growth temperature, that is, the melting point is usually about 2000 ° C. In such a high temperature atmosphere, RuO ₂ , Rh ₂
Transition metal oxides such as O ₃ are easily converted to metal Ru or metal R
Decomposes into h and oxygen. The decomposition reaction proceeds at a temperature lower than the melting point of RuO ₂ or Rh ₂ O _{3 in} air at about 1 atm. However, RuO ₂ → Ru + O ₂ or Rh ₂ O ₃ → R
The decomposition reaction of h + O ₂ is strongly affected by the oxygen partial pressure of the atmosphere.

As for the relationship between the equilibrium vapor pressure and the temperature for the reaction of RuO ₂ → Ru + O ₂ , various equilibrium vapor pressure-temperature curves have been reported as shown in FIG. Chatterji and R.S. W. Vest,
J. Am. Ceram. Soc. , 54 [2] 73 (1
971) and (b) show S.E. Pizzini and L.M.
Rossi, Z .; Natureforsch. , 26A
[1] 177 (1971); E. FIG. Bell
and M.M. Tagami, J .; Phys. Che
m. , 67 [11] 2432 (1963), and (d) show V.I. K. Tagirov, D .; M. Chizhiko
v, E .; K. Kazenas, and L.M. K. Shu
Bochkin, Zh. Neorg. Khim. , 20
[8] 2035 (1975); Russ. J. Inor
g. Chem. (Engl. Transl.), 20
[8] 1133 (1975)]. Rh ₂ O ₃ → Rh + O
_As for the relationship between the equilibrium vapor pressure and the temperature for the reaction of Example 2, various equilibrium vapor pressure-temperature curves have been reported as shown in FIG. 2 [V. K. Tagirov, D .; M. Chi
Zhikov, E .; K. Kazenas, and L .;
K. Shubochkin, Zh. Neorg. Khi
m. , 20 [8] 2035 (1975); Russ.
J. Inorg. Chem. (Engl. Trans
l. ), 20 [8] 1133 (1975)].

Therefore, in the present invention, RuO_Two → R
u + O_Two And Rh_Two O_Three → Rh + O_TwoAffects the decomposition reaction of
By adjusting the oxygen partial pressure of the growing atmosphere
uO _Two , Rh_Two O_Three Of RuO as raw material_Two 
And Rh_Two O_Three Maintain a stable oxide state. concrete
The oxygen partial pressure of the growing atmosphere should be maintained at about 10 to 15 atm.
Holding it, even under high temperature conditions of about 2000 ° C_Two ,
Rh_Two O_Three Exists stably. Therefore, RuO_Two ,
Rh_Two O_Three Transition metal oxides maintained a stable state
Melts with other raw materials by the floating zone method as it is
Grows as a single crystal. As a result, the target transition gold
A large single crystal of a group oxide can be produced. Rh_Two O_Three During ~
And the formal valence of Rh is trivalent, but Sr_Two RhO_Four , C
a_Two RhO_Four , SrRhO_Three , CaRhO_Three , Sr_Three R
h_Two O₇ , Ca_Three Rh_Two O₇ In the formal valence of Rh is
It is tetravalent. In this case, the oxide single crystal to be grown
Of transition metal element T in raw material and raw material oxide T_x O_y (_x ,
_y Is a positive integer) and the valences of T in T
However, it is only necessary to comply with it.

[0010]

EXAMPLES The present invention will be specifically described with reference to the growth of a single crystal of SrRuO ₃ as an example. SrCO ₃ and RuO ₂ were mixed at a molar ratio of 1: 1.2, mixed finely and thoroughly with an agate mortar, formed into pellets, and dried at 1200 ° C. in air at 12 ° C.
Sintered for hours. During sintering, SrCO ₃ decomposes and C becomes CO
_It was separated by evaporation as ₂ . The sintered body was pulverized and mixed again, pressed and shaped into a rod having a diameter of 6 mm and a length of 100 mm, and sintered in air at 1300 ° C. for 6 hours to prepare a raw material rod for the sintered body. The raw material rod was set in an image furnace equipped with a halogen lamp and a bi-elliptical reflecting mirror, and oxygen at 10 atm was introduced into the space of the raw material rod. While supplying oxygen at a flow rate of 100 cc / min so that a constant oxygen partial pressure was maintained during the growth, the lamp voltage was increased until the raw material rods began to melt, and the voltage was maintained constant after the start of melting. The input power at this time was about 3 kW. By lowering the molten raw material from the lamp focal position, the molten raw material rod was slowly cooled to grow a desired single crystal. The obtained oxide single crystal had a diameter of 5 mm and a length of 100 mm. In principle, it is possible to produce a single crystal having a diameter of about several centimeters by the same growing method, and it can be used as a functional material such as a magneto-optical material or a substrate for growing a thin film.

[0011]

As described above, in the present invention,
Means that an oxide containing Ru or Rh as a transition metal is stable
Maintain oxygen partial pressure, maintain RuO_Two → Ru + O_Two 
And Rh _Two O_Three → Rh + O_Two While suppressing the decomposition reaction of
Single crystals of transition metal oxides are grown by the floating zone method.
When using this method, transition metal oxidation caused by decomposition reactions
Transition metal oxides with target composition
Crystals are produced under stable conditions. Moreover, large single crystal
It can be used as a substrate for growing various functional materials and thin films.
Used in a wide range of fields.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between RuO ₂ / Ru equilibrium vapor pressure and temperature.

FIG. 2 is a graph showing the relationship between the equilibrium vapor pressure of Rh ₂ O ₃ / Rh and the temperature.

Claims (3)

(57) [Claims] When growing a single crystal of an oxide containing Ru or Rh as the transition metal element T, the target transition metal oxide has the same valence as the valence of the transition metal element T or a valence equivalent thereto. oxide T _x O _y containing a transition metal element T
A method for growing a transition metal oxide single crystal, characterized in that the growth atmosphere is adjusted to an oxygen partial pressure where ( x and y are positive integers) can be stably present at the growth temperature. 2. RuO ₂ , SrRuO ₃ , CaRuO
₃ , Ca ₂ RuO ₄ , Sr ₃ Ru ₂ O ₇ , Ca ₃ Ru ₂
O ₇ , Rh ₂ O ₃ , Sr ₂ RhO ₄ , Ca ₂ RhO ₄ ,
SrRhO ₃ , CaRhO ₃ , Sr ₃ Rh ₂ O ₇ , Ca
When growing one transition metal-containing oxide single crystal selected from ₃ Rh ₂ O ₇ by the floating zone method, RuO ₂ or Rh
_A method for growing a transition metal oxide single crystal, comprising adjusting a growth atmosphere to an oxygen partial pressure at which ₂ O ₃ can be stably present at a growth temperature. 3. The method of growing a transition metal oxide single crystal according to claim 1, wherein the oxygen partial pressure of the growing atmosphere is maintained at 10 to 15 atm.